However, he stressed that Marouane Fellaini is available despite the midfielder leaving training early on Sunday after being kicked on his calf.

Red Devils captain Kompany has been battling a groin injury and sat out Belgium's final group stage game against South Korea on June 26.

Speaking at his prematch news conference at the Arena Fonte Nova, Wilmots added that Kompany was scheduled to train with the side later on Monday, at which point he would get a clearer picture of the defender's health.

"Kompany will train for 90 minutes and then we will see in the morning how he responds," Wilmots said. "There is a 50-50 chance that he'll play. I know his injury. I played for a year with the same problem."

He suggested that the Manchester City centre-back would make the final decision, adding: "I used to have a very good, trusting relationship with [former Standard Liege and Belgium boss] Robert Waseige. If I said I could play, he would follow my assessment. I have the same relationship with Vincent."

"Vermaelen is on schedule to play in the quarterfinals if we get there," he said. "Right now he is rehabilitating, he's running and sprinting. In two or three days, [Vermaelen] can have the collective training, but he cannot play against the U.S."

On Fellaini, he said: "With Marouane I don't see any problem, none whatsoever."

If Kompany and Vermaelen are both unable to play, Belgium are likely to field Nicolas Lombaerts alongside Daniel Van Buyten in central defence.

Belgium will also be without Steven Defour for the match following his red card against South Korea but FIFA has decided against extending his suspension.

Defour was dismissed for a studs-up challenge on South Korea striker Kim Shin-Wook during his side's 1-0 victory and could have faced an extended ban.

However, FIFA's disciplinary committee was satisfied with the one-match ban, although the Porto midfielder has been fined 7,500 Swiss francs (4,943 pounds) for breaching the governing body's disciplinary code